1. Field of the Invention
The present invention relates to a planar lighting device of a kind having a light source disposed in a side edge of a light guide plate.
2. Description of Related Art
Planar lighting devices for providing a planar illumination have hitherto been made available in the market, of a structure, in which rays of light from a light source are introduced into a light guide plate of a flat plate configuration, having a predetermined surface area, and an object to be lighted such as, for example, a liquid crystal display device is illuminated in plane from rear. Of those planar lighting devices, a planar lighting device of a down lighting system, in which the light source is disposed rearwardly of the light guide plate, and the planar lighting device of a so-called side edge system, in which the light source is disposed in a side edge of the light guide plate, are particularly well known in the art.
Of them, the planar lighting device of the side edge system is particularly advantageous in that as compared with the planar lighting device of the down lighting system, the planar lighting device as a whole can have a reduced thickness and can be structured to exhibit a space saving.
On the other hand, with the planar lighting device of the side edge system there has been a problem in that a base dedicated for the light source is required and, also a space is required for installation of the light source and the base at a side portion of the light guide plate. As a result, downscaling of the planar lighting device in a widthwise direction tends to be hampered.
In order to alleviate the problem underlying the planar lighting device of the side edge system discussed above, the Japanese Laid-open Patent Publication No. 2001-222905 (Patent Document 1) suggests that the light source is disposed below the light guide plate and a portion of the light guide plate proximate to one side edge thereof is curved so as to confront the light source.
The structure of the component parts of the planar lighting device 110 includes, as shown in FIG. 4a, a transparent substrate 111, an electric wiring substrate (base) 115 and an elongated light source 118. The light source 118 has a light guide member 114 of an elongated shape disposed on the base 115, a spot light source 116 comprised of a light emitting diode (LED) and a reflecting member 113. One side end portion 112 of the transparent substrate 111 is bent to hang downwards so that rays of light from the light source 118 can be introduced into the planar substrate 111.
In the planar lighting device 110 so constructed as hereinabove, as shown in FIG. 4b, a sectional view, rays of light emitted from the spot light source 116 are introduced from one side end portion 112 into the transparent substrate 111 through the light guide plate 114 and propagate within the transparent substrate 111, while having repeated a diffused reflection, to illuminate in a plane. As such, there is no need to dispose the light source and the base dedicated for the light source at the side edge of the light guide plate, which has been the problem underlying the planar lighting device of the side edge system.